1. Field of the Invention
An aspect of the present invention relates to an image forming apparatus, and, more specifically, the invention relates to an image forming apparatus on which a developing unit may be relatively easily mounted.
2. Description of the Related Art
Generally, an electro-photographic image forming apparatus, such as a laser beam printer, is an apparatus that forms an electrostatic latent image on a photosensitive medium such as a photosensitive drum or a photosensitive belt, and obtains a desired image by developing the electrostatic latent image with a certain colored developer and transcribing that electrostatic latent image onto a recording medium. Meanwhile, in recent image forming apparatuses, reductions in apparatus sizes and decreases in medium costs have been possible where a cover is opened in order to be used as a paper feeding plate instead of a cassette-type recording medium feed cover.
FIG. 1 is a schematic view showing a developing unit mounting structure of a conventional image forming apparatus, and FIG. 2 is a perspective view explaining a developing unit mounting structure of a conventional image forming apparatus. Referring to FIGS. 1 and 2, an image forming apparatus is shown as comprising a main body 1, a cover 3, and a developing unit 5. One end portion of the cover 3 is coupled, in a pivoting manner, to one side surface of the main body 1 so that an opening la is opened and closed. The cover 3 is configured to be able to supply recording media as well by allowing for a stacking of recording media on the top surface thereof while the cover 3 is opened. Hereafter, the cover is called a “recording medium feed cover”. A stopper 7 to align recording media in a lengthwise direction thereof is installed on the top of the recording medium feed cover 3 in order to move rectilinearly along the direction of the X-axis of FIGS. 1 and 2. In addition, recording medium width guides 9 to align recording media in the widthwise direction thereof are installed at both sides within the main body 1 so as to move rectilinearly along the direction of the Y-axis of FIGS. 1 and 2. Here, a recording medium cover 11 is installed in order to prevent foreign particles from falling on recording media when the recording medium feed cover 3 is opened and recording media are stacked.
The developing unit 5 to form images on the recording media supplied from the recording medium feed cover 3 is formed with a cartridge 5a that has a toner container containing a large amount of toner and a developing chamber to form images on the supplied recording media using the toner transferred from the toner container. Generally, a photosensitive medium (not shown) that rotates at a certain speed is installed inside the developing chamber, and a charging roller (not shown) to charge the surface of the photosensitive medium with a certain voltage is installed at one side of the photosensitive medium. In addition, at the other side of the photosensitive medium, a developing roller (not shown) is installed to apply toner on the surface of the photosensitive medium where an electrostatic latent image is formed and to develop the electrostatic latent image into a visible image.
As is described above, the developing unit 5 is integrated into one cartridge 5a. Accordingly, when the cartridge is used up and needs to be replaced with a new cartridge, or when jammed paper is removed, users may replace the cartridge themselves. A handle 5b is formed at one end of the cartridge 5a so that the cartridge may be easily mounted. Here, guide rails 1b to guide the transfer of the developing unit 5 are formed at both sides within the main body 1 in order to allow for a replacement of the developing unit 5, and guide projections 5d are formed at both sides of the developing unit 5 to cooperate with the guide rails 1b. 
When a user replaces the developing unit 5 or removes jammed recording media, the user opens the opening 1a of the main body 1 by opening the recording medium feed cover 3, and holds the handle 5b of the developing unit 5 and thereby pulls the developing unit 5 out of the main body 1. Thereafter, when a new developing unit 5 is mounted, or when the existing developing unit is put back into an original position thereof, after a removal of the jammed recording media, as shown in FIG. 1, the guide projections provided at both sides of the developing unit 5 are set on the guide rails 1b, and the developing unit 5 is pushed inside the main body 1.
However, at this point, in a case where a user does not correctly set the guide projections 5d to the guide rails 1b, the developing unit 5 cannot be mounted correctly. On the other hand, even if the developing unit is mounted by force, normal printing operations cannot be performed.